Industry is trending towards using more and more lightweight materials such as aluminum alloys to build vehicle body structures as a result of the increasing demand for fuel efficient vehicles. Resistance spot welding is the leading joining technology for steel parts. Resistance spot welding is not the preferred solution for joining aluminum parts because weld quality problems, substantial fixed costs for tooling and welding systems, and high energy demands.
Self-piercing rivets are used in some joining applications where aluminum parts are joined together or with dissimilar parts. However, self-piercing rivets may not be the ideal solution for all aluminum alloys and are relatively costly.
Friction stir spot welding is a technique that is used in production to join aluminum or steel parts together. The use of friction stir spot welding may reduce energy consumption by over 90% compared to resistance spot welding on the same parts. Substantial cost savings can be achieved with the use of friction stir spot welding. However, C-Type gun friction stir spot welding technology tends to be limited to making sub-assemblies and assemblies having weld points that are located around the periphery of the parts.
One challenge to making friction stir spot welding and self-piercing rivets viable solutions for joining a wider variety of aluminum parts is reducing the large axial load required to plasticize the material. Another challenge for friction stir spot welding is the difficulty of firmly clamping the body elements during joining. In general, friction stir spot welding requires higher loading of the gun compared to welding guns used for resistance spot welding. Load management is a key driver to the implementation of friction stir spot welding technology. A relatively high clamping load is required during friction stir spot welding to maintain proper mixing of plastisized material and to avoid full or partial separation of the parts being welded which may result in a poor weld.
In addition, the wide range of part geometries that can be encountered in automotive production make it difficult to clamp parts together while performing a friction stir spot welding operation.
The above problems and challenges are addressed by this disclosure as summarized below.